Condensation behaviors and resulting heat transfer performance of nano-engineered copper surfaces

We report the microscopic condensation behaviors and resulting heat transfer performance of scalable Cu-based water repellent surfaces with different wetting characteristics including hydrophobic (HPo), superhydrophobic (SHPo) and oil-infused superhydrophobic (Oil-SHPo). The overall heat transfer coefficient and the heat transfer rate through an individual droplet are investigated on horizontally-placed surfaces using the humidity and temperature controlled high speed microscopy combined with thermal network based model. The results show that the average heat transfer rate through an individual droplet is about an order of magnitude smaller on SHPo than on HPo or Oil-SHPo mainly due to smaller droplet radius and higher contact angle. However the investigated SHPo can provide a high number density of condensates throughout the entire measurement via coalescence-induced jumping, while HPo or Oil-SHPo rapidly loses their number density during the droplet coalescence which makes ​the suggested SHPo a promising condenser for long term use. After ∼300 min, the overall heat transfer coefficient of the suggested SHPo becomes ∼60% higher than that of HPo and Oil-SHPo. This work clarifies the heat transfer performance of water repellent condensers with different wetting characteristics, and helps develop optimized condensers.